The present invention relates to an eyepiece optical system which can be applied to a head/face fitting visual display device, and an eyepiece image (video) display device equipped with it. The eyepiece optical system can be held at a user's head or face.
In recent years, for the purpose of "virtual reality" or personally enjoying a large-screen image, visual display devices of a helmet type or goggle type which are held at a user's head or face have become available. For example, one of them is to enlarge a image on a small display element such as a liquid display element, an EL display element, etc. and project it onto an eyeball through an eyepiece optical system such as a lens. The optical system for such an eyepiece visual display device is shown in FIG. 27. In FIG. 27, reference numeral 3 denotes a two-dimensional display element; 20 an eyepiece lens for enlarging and projecting it in the air; and 10 denotes eyeballs of an observer. In a conventional device, the enlarged virtual image of an original image formed on two-dimensional display devices 3 is formed and appreciated by an eyeball 10.
An example of the conventional technique for an eyepiece optical system is an eyepiece lens such as a microscope, binoculars, telescope, finder, etc. (the Examined Japanese Utility Model Application Publication No. Sho 40-9090, the Unexamined Japanese Patent Application Publication No. Sho 50-151163, the Unexamined Japanese Patent Application Publication No. Sho 51-120231, the Unexamined Japanese Patent Application Publication No. Sho 52-72242, and the Unexamined Japanese Patent Application Publication No. Hei 3-87709).
In order to improve the fitting capability of a head/face fitting visual display device, it is important to reduce the entire size of the device and the weight thereof. Assuring a large view angle is required to enhance the presence of a screen. It is not too much to say that the presence is critically dependent on the view angle provided. It is desired that a display view angle of 100.degree. or more in an opposite angle is realized to give the presence such as an three-dimensional effect, intensity, immersing sense, etc. to an observer.
Further, a designed small pupil diameter at an eye point in a eyepiece system leads to a freedom of pupil so that slight deviation of the pupil from an optimum fitting state of the device results in a dark area on the periphery of the observed field of view, thus impairing the sense of reality. Therefore, it is required to reduce the F-number in an eyepiece optical system.
However, if the view angle in the eyepiece optical system is increased and the F-number is decreased, much aberration occurs because light passes the periphery of the optical system. This makes it difficult to correct the aberration in a compact configuration and lowers the resolution of a peripheral image under the influence of curvature of field. Particularly, it is difficult to correct the curvature of field since in the eyepiece lens having a smaller number of lenses, a positive lens is located at a high light-ray position and a negative lens is located at a low light-ray position to reduce the Petzval sum in distribution of positive and negative power.
The eyepiece optical system provided by the present invention satisfies the following conditions simultaneously:
(1) a large view angle of 110.degree. or more in an opposite angle PA1 (2) a small F number (large pupil diameter) PA1 (3) a suitable eye relief (distance from the eye of an observer to the first surface of the eyepiece lens) PA1 (4) good aberration correction
On the other hand, although the conventional eyepiece lens assures a relatively large view angle of 50.degree. to 70.degree., it cannot satisfy the above conditions indispensable to realize sufficient realism or presence and easiness in practical use in applications such as "virtual reality". Therefore, equipping an eyepiece image display device with the above conventional eyepiece lens cannot provide a large observation view angle, large freedom of pupil position and flat clear image to the periphery.